Switchable sign

Abstract

A traffic sign selectively displays and obscures information arranged permanently on the outer surface of a rear plate of a pair of rigid, transparent plates defining a closed cavity therebetween by displacing out of and into the cavity an opaque liquid contained in a closed reservoir which has an air-filled space over the liquid. A closed fluid conduit system connects the cavity with the reservoir and includes a first valved conduit connecting the air-filled space to the cavity, a second valved conduit connecting the liquid to the reservoir, a pressure release valve in the first conduit, and a control for selectively delivering liquid from the reservoir into the cavity through the second conduit while concomitantly withdrawing air from the cavity through the first conduit, and vice versa, whereby the cavity is rapidly and completely filled with the liquid to obscure the information and emptied of the liquid to display the information. The information is illuminated from the rear.

What we claim is: 
     
       1. A sign for selectively displaying information to a viewer and obscuring the information from the viewer looking at the sign from one direction, which comprises a. a pair of rigid and light-transmitting plates of an acrylic resin arranged parallel to each other and interconnected at respective edges thereof to define a closed cavity of constant volume between the inner, facing surfaces of the plates, the outer surface of a front one of the plates facing the viewer and the outer surface of a rear one of the plates facing in a direction opposite to the one direction, 1. the information being arranged permanently on the outer surface of the rear plate,     b. a plurality of rigid pins interconnecting the facing surfaces of the plates, the pins being of light-transmitting material and supporting the plates against deformation,   c. a closed reservoir containing a liquid substantially impervious to the transmission of light, the liquid being liquid petrolatum having a freezing point of -54° C., a fast and light-impervious dye homogeneously dissolved therein and an anti-static agent dispersed therethrough, and an air-filled space over the liquid,   d. a closed fluid conduit system connecting the closed cavity and closed reservoir, the conduit system including 1. a first valved conduit connecting the air-filled space to the cavity,   2. a second valved conduit connecting the liquid to the cavity,     
     
     
       3. a pressure release valve in the first conduit, and 4. control means for selectively delivering liquid from the reservoir into the cavity through the second conduit while concomitantly withdrawing air from the cavity into the air-filled spaced through the first conduit, and delivering air from the space into the cavity through the first conduit while concomitantly withdrawing liquid from the cavity into the reservoir through the second conduit, whereby the cavity is rapidly and completely filled with the liquid to obscure the information and emptied of the liquid to display the information, and   e. a light source mounted behind the rear plate in said one direction for illuminating the information.   
     
     
       2. The sign of claim 1, wherein the control means comprises a pump in the fluid conduit system, the pump being reversible for selectively pumping liquid into the cavity while concomitantly pumping air out of the cavity and pumping air into the cavity while concomitantly pumping liquid out of the cavity, and solenoid valve means in the fluid conduit system, the valve means being operable selectively to open and close a respective one of the conduits for permitting the air and liquid to pass or to be retained. 
     
     
       3. The sign of claim 2, wherein the valve means consists of four solenoid valves, a first one of the valves being mounted in the second conduit, the first conduit including a first branch, a second branch and a by-pass interconnecting the first and second branches, the pump is mounted in the second branch between the by-pass and the air-filled space, a second one of the valves is mounted in the second branch between the by-pass and the cavity, a third one of the valves is mounted in the by-pass, and a fourth one of the valves is mounted in the first branch between the by-pass and the air-filled space, the four valves being operable to be closed in a rest position wherein the cavity is filled with the liquid or with air, the first and third valves to be opened and the pump started in a filling position wherein the cavity is to be filled with liquid and emptied of air, while the second and fourth valves remain closed, and the second and fourth valves to be opened and the pump started in an emptying position wherein the cavity is to be filled with air and emptied of liquid, while the first and third valves remain closed. 
     
     
       4. The sign of claim 1, further comprising a casing attached to the pair of rigid plates and defining a chamber with the rear plate, means for mounting the reservoir in the casing chamber, and the conduit system and light source being arranged in the casing chamber. 
     
     
       5. The sign of claim 1, comprising more than one set of pairs of rigid plates, the sets being coplanar, each of the sets having a respective one of the conduit systems and light sources, and the reservoir being connected to the closed cavity of each set through the respective conduit systems. 
     
     
       6. The sign of claim 1, wherein the rigid pins are of the same acrylic resin as the plates, the plates and pins forming an integral double-walled structure reinforced by the pins.